Gas generating composition

ABSTRACT

A solid composition capable of self-sustained combustion to produce gaseous nitrogen and nonvolatile solids as its combustion products comprises a mixture of a first metal azide and the oxide or salt of a second metal which second metal is below the first metal in the electrochemical series and which is capable of being substituted by the first metal in the oxide or salt. Many combinations of various components may be used, but some care is required to select only those combinations in which the solid products are nonvolatile at the temperatures encountered during the combustion. A representative system employes iron oxide and sodium azide according to the following reactions: 
     
         Fe.sub.2 O.sub.3 +6NaN.sub.3 →2Fe+3Na.sub.2 O+9N.sub.2 ↑ 
    
     Another embodiment of the invention generates mixtures of nitrogen and other gases such as carbon dioxide, carbon monoxide and/or water particularly suitable for use in lasers. This is accomplished by adding to the mixture materials which react or decompose into the desired gases. If carbon monoxide or carbon dioxide is the desired additional gas, a metal carbonate may be used as the salt in the above reaction.

BACKGROUND OF THE INVENTION

There are many applications which require a storable source of gaseous nitrogen which may be used for a variety of pressurization or purging applications, for example. Nitrogen is inert with respect to many oxidizers, including the high energy interhalogen compounds such as ClF₃ and ClF₅, fluorine, oxygen, or various nitric acid compositions such as red fuming and white fuming nitric acid and many fuels such as hydrogen, hydrazine, kerosene, or other hydrocarbons. Thus, in rocket motors for example, it is possible to use nitrogen to pressurize or purge both fuel and oxidizer tanks. Nitrogen is also used in space station and vehicle atmospheres as a diluent for the oxygen. Thus, in the event of leakage not only will oxygen but also nitrogen will be lost and a storable means of replenishing nitrogen in the event of leaks is required. Nitrogen gas is also used in many laser applications and a storable source of gaseous nitrogen would be highly desirable, particularly for portable and military operations. In laser applications for example, it is also desirable that nitrogen contain amounts of other gases such as carbon dioxide, carbon monoxide or water.

There are three basic ways of storing nitrogen, i.e., as a gas, as a liquid, or chemically combined in a manner in which it can be controllably released. Storage as either gas or liquid is done by state-of-the-art techniques, but is associated with the problems inherent to pressurized gases or cryogenic liquids. A substantial body of art, therefore, has been developed towards making so-called nitrogen "candles" which are combustible compositions capable of liberating gaseous nitrogen. Such a composition is represented by U.S. Pat. No. 2,981,616 to Boyer for a Gas Generator Grain. The composition of this patent utilize a metal azide as a source of the nitrogen and an amount of oxidizing agent selected from the class of metal peroxides, inorganic perchlorates and metal nitrates in amounts sufficient to fully oxidize the metal component of the azide. Such compositions are capable of producing nitrogen gas, however, they are relatively energetic systems which can present safety hazards from inadvertent ignition. Further, these oxidizing agents produce high flame temperatures in the combustion process and in many cases the nitrogen gas evolved must be subsequently treated to cool it to a usable temperature and in some cases the temperature may also be so sufficiently high as to produce volatilization of some of the normally solid reaction products.

DESCRIPTION OF THE INVENTION

According to this invention, novel gas generator compositions have been discovered which have substantially no impact or friction sensitivity and which produce nitrogen gas or nitrogen mixed with other gases as the only volatile products at relatively low flame temperatures.

The desirable features of this invention are obtained by reacting metal azides with various metal oxides and salts as the oxidative reactant. To permit self-sustained combustion, the metal forming the azide should be sufficiently above the metal of the oxide or salt in the electromotive series of the elements so that the metal of the azide is capable of exothermically replacing the metal of the oxide or salt. To prevent the liberation of volatiles, other than the desired gases, the metal oxide or salt must be selected such that the residue produced by the reaction consists only of materials which are non-volatile under the reaction conditions. The general reaction sequence may be shown as follows: metal₁ azide+metal₂ oxide (or salt)→metal₁ oxide(or salt)+metal₂ +nitrogen

In the above reaction metal₁ is a metal which is higher in the electromotive series of the elements than metal₂ and is capable of replacing the metal₂ exothermically in the above general reaction scheme and the stoichiomety of the system is preferably adjusted to permit maximum liberation of the nitrogen of the azide and of metal₂ together with the total substitution of metal₁ in the oxide or salt.

The addition of a hydrogen-free carbon compound and an oxidizing agent for the carbon in amounts sufficient to convert desired amounts of carbon monoxide to carbon dioxide may be made to the compositions of this invention to permit the generation of nitrogen - CO₂ mixtures for use in lasers. Suitable carbon compounds include, without being limited to, carbonates, metal oxalates such as Li₂ C₂ O₄, Na₂ C₂ O₄, and MgC₂ O₄ and carbon-nitrogen compounds such as tetracyanoethylene (C6N₄).

Elimination or reduction of the additional oxidizer will result in the evolution of carbon monoxide. Addition of hydrated materials or basic oxides such as Mg(ClO₄)₂.6H₂ O, FeO₂ H, oxamide and oxalic acid dihydrate either alone or in conjunction with the carbon compound will generate water. The formulas for oxamide and oxalic acid dihydrate are respectively (CO.NH₂)₂ and (COOH)₂.2H₂ O.

Representative theoretical chemical reactions by which these gases may be generated are set forth below:NITROGEN GENERATORS6NaN₃ + Fe₂ O₃ → 3Na₂ O + 2Fe + 9N₂12NaN₃ + 3SiO₂ → 6Na₂ O + Si₃ N₄ +16N₂6LiN₃ + B₂ O₃ → 3Li₂ O + 2BN + 8N₂6KN₃ + Fe₂ O₃ → 3K₂ O + 2Fe + 9N₂4LiN₃ + TiO₂ → 2Li₂ O + Ti + 6N₂3NaN₃ + 3LiCl→ Li₃ N + 3NaCl + 4N₂6NaN₃ + 2AlF₃ → 6NaF + 2AlN + 8N₂3NaN₃ + 3LiF→ Li₃ N + 3NaF + 4N₂6NaN₃ + 3CuCl₂ → 6NaCl + 3Cu + 9N₂6NaN₃ + Fe₂ (SO₄)₃ → 3Na₂ SO₄ + 2Fe+ 9N₂2NaN₃ + FeS→ Na₂ S + Fe + 3N₂2NaN₃ + FeCO₃ → Na₂ CO₃ + Fe + 3N₂12NaN₃ + 3CaMg(CO₃)₂ → 6Na₂ CO₃ +Ca₃ N₂ + Mg₃ N₂ + 16N₂NITROGEN-CARBON DIOXIDE GENERATORS6NaN₃ + 9FeCO₃ → 3Na₂ CO₃ + 9FeO + 9N₂ +3CO + 3CO₂16NaN₃ + 4SiO₂ + 15MgCO₃ → 8Na₂ CO₃ +Si₄ N₃ + 15MgO + 27N₂ + 7CO₂2NaN₃ + Fe₂ O₃ + 2FeCO.sub. 3 → Na₂ CO₃ +4FeO + 3N₂ + CO₂8NaN₃ + 10FeCO₃ + 2NaNO₃ + 2FeO₂ H→ 5Na₂CO₃ + 2Fe₂ O₃ + 8FeO + 13N₂ + H₂ O + 5CO₂10NaN₃ + 9MgCO₃ + 0.17Mg(NO₃)₂.sup.. 6H₂ O +1.04 NaClO₄ → 5Na₂ CO₃ + 9.17 MgO + 15.17 N₂ +4CO₂ + 1.02H₂ O + 1.04NaCl8NaN₃ + 1.2C₆ N₄ + 0.3(COOH)₂.sup.. 2H₂ O + 4.75NaClO₄ → 4Na₂ CO₃ + 4.75 NaCl + 0.9H₂ O +3.8CO₂ + 14.4N₂

Table I sets forth the results of tests on various gas generator compositions.

                                      TABLE I                                      __________________________________________________________________________     (A) Compositions of Pelletized Propellants - no                                Reinforcing Fiber                                                              Mole                                                                           %  Component                                                                             Mole                                                                               Component                                                                             Mole                                                                              Mole   Solid Residue                                                                            Ignition & Combus-                                                                            Combustion             NaN.sub.3                                                                           (1)  %     (2)  %  Ratio Reaction Products                                                                          tion Behavior Temperature            __________________________________________________________________________     60.0                                                                              AlF.sub.3                                                                             40.0                                                                                --    -- 3/2   Na.sub.3 AlF.sub.6 +AlN                                                                   ignited-slow burning                                                                          940                                                             rate                                  85.7                                                                              Al.sub.2 O.sub.3                                                                      14.3                                                                                --    -- 6/1   Na.sub.2 O+AlN                                                                            no ignition with                                                                               ---                                                            tained burning                        85.7                                                                              Al.sub.2 O.sub.3                                                                       8.7                                                                               Fe.sub.2 O.sub.3                                                                      5.6                                                                               ˜77/8/5                                                                        Na.sub.2 O+Fe+AlN                                                                         ignited-moderate                                                                              1020-1090                                            Na.sub.2 Fe.sub.2 O.sub.4 (?)                                                             burning rate                          85.7                                                                              B.sub.2 O.sub.3                                                                       14.3                                                                                --    -- 6/1   Na.sub.2 O+BN                                                                             slow to ignite-moderate                                                                       830                                                             burning rate                          49.2                                                                              CaCO.sub.3                                                                            36.5                                                                               FeO.sub.3                                                                             14.3                                                                              ˜17/13/5                                                                       Na.sub.2 O+CaO+Fe                                                                         ignited-moderate                                                                               --n-                                                           ing rate                              50.0                                                                              CuCl   50.0                                                                                --    -- 1/1   NaCl+Cu    ignited-very rapid                                                                            686n-                                                           ing rate                              66.7                                                                              CuO    33.3                                                                                --    -- 2/1   Na.sub.2 O+Cu                                                                             ignited-moderate                                                                              >1200                                                           ing rate                              85.7                                                                              Fe.sub.2 O.sub.3                                                                      14.3                                                                                --    -- 6/1   Na.sub.2 O+Fe                                                                             ignited easily-good                                                                           940                                                             burning rate                          66.4                                                                              FeCO.sub.3                                                                            33.6                                                                                --    -- 2/1   Na.sub.2 CO.sub.3 +Fe+FeO                                                                 ignited-fairly                                                                                 --id                                                           burning rate                          88.9                                                                              Fe.sub.3 O.sub.4                                                                      11.1                                                                                --    -- 8/1   Na.sub.2 O+Fe                                                                             ignited-moderate                                                                              ˜566                                                      ing rate                              85.7                                                                              Fe.sub.2 (SO.sub.4).sub.3                                                             14.3                                                                                --    -- 6/1   Na.sub.2 SO.sub.4 +Fe                                                                     ignited-moderate                                                                               --n-                     1.sub.nH.sbsb.2O 3                    ing rate                              66.7                                                                              FeS    33.3                                                                                --    -- 2/1   Na.sub.2 S+Fe                                                                             ignited-fairly                                                                                 --id                                                           burning rate                          49.5                                                                              L.sub.1 Cl                                                                            50.5                                                                                --    -- 1/1   NaCl+Li.sub.3 N                                                                           ignited (after                                                                                 --ydration)           moderate burning rate                                                          49.8                                                                              LiF    50.2                                                                                --    -- 1/1   NaF+Li.sub.3 N                                                                            ignited-extremely                                                                              --w                                                            burning rate                          88.8                                                                              Li(CO.sub.2).sub.2                                                                    11.2                                                                                --    -- 8/1   Na.sub.2 O+Li.sub.3 N                                                                     ignited-moderate                                                                               --ning                                                         rate                                  66.6                                                                              Li.sub.2 SO.sub.4                                                                     33.5                                                                                --    -- 2/1   Na.sub.2 SO.sub.4 +Li.sub.3 N                                                             ignited, but not                                                                               --tained                                                       combustion                            46.4                                                                              MgCO.sub.3 .×H.sub.2 O                                                          53.6                                                                                --    -- ˜1/1                                                                           Na.sub.2 CO.sub.3 +Mg.sub.3 N.sub.2                                                       no ignition with                                                                               --tained                                                       burning                               61.3                                                                              MgCO.sub.3.×H.sub.2 O                                                           38.7                                                                                --    -- ˜3/2                                                                           Na.sub.2 CO.sub.3 +Mg.sub.3 N.sub.2                                                       ignited-extremely slow                 --                                                                                                                     burning rate                          80.0                                                                              MnO.sub.2                                                                             20.0                                                                                --    -- 4/1   Na.sub.2 O+Mn                                                                             ignition difficult-moderate                                                                   740                                                             burning rate                          80.0                                                                              SiO.sub.2                                                                             20.0                                                                                --    -- 4/1   Na.sub.2 O+Si.sub.3 N.sub.4                                                               ignited easily-fairly                                                                         760id                                                           burning rate                          75.0                                                                              SiO.sub.2                                                                             25.0                                                                                --    -- 3/1   Na.sub.2 SiO.sub.3                                                                        ignited-fair to                                                                               893erate                                                        burning rate                          (B) Compositions of Molded Propellants -                                       Fiberglass Binder (1 wt %)                                                     Mole                                                                           %  Component                                                                             Mole                                                                               Component                                                                             Mole                                                                              Mole   Solid Residue                                                                            Ignition & Combus-                    NaN.sub.3                                                                           (1)  %     (2)  %  Ratio Reaction Products                                                                         tion Behavior                         __________________________________________________________________________     56.4                                                                              AlF.sub.3                                                                             43.6                                                                                --    -- 4/3   NaAlF.sub.4 (?)+NaF                                                                       ignited-moderate burning                                                       rate                                  21.0                                                                              AlO.sub.3                                                                             10.5                                                                               SiO.sub.2                                                                             68.4                                                                              12/6/37                                                                              Na.sub.2 O.Al.sub.2 O.sub.3.6SiO.sub.2                                                    no ignition with sustained                                           silicate  burning                               20.3                                                                              Al.sub.2 O.sub.3                                                                       4.9                                                                               SiO.sub.2                                                                             74.8                                                                              ˜25/6/90                                                                       Na.sub.2 O.Al.sub.2 O.sub.3.6SiO.sub.2                                                    no ignition with sustained                                           silicate  burning                               42.0                                                                              Al.sub.2 O.sub.3                                                                       7.8                                                                               SiO.sub.2                                                                             50.2                                                                              ˜24/6/39                                                                       Na.sub.2 O.Al.sub.2 O.sub.3.6SiO.sub.2                                                    ignited, but very slow                                               silicate  burning rate                          83.3                                                                              Al.sub.2 O.sub.3                                                                       6.1                                                                               SiO.sub.2                                                                             10.6                                                                              13.7/1/1.7                                                                           sodium ferrate or                                                                         ignition easy-good burning                                          sodium aluminate                                                                          rate                                  61.9                                                                              Al.sub.2 O.sub.3                                                                      12.9                                                                               Fe.sub.2 O.sub.3                                                                      25.2                                                                              ˜4.8/1/2                                                                       sodium ferrate or                                                                         ignited-less rapid burning                                          sodium aluminate                                                                          rate                                  69.9                                                                              Al.sub.2 O.sub.3                                                                      18.7                                                                               Fe.sub.2 O.sub.3                                                                      11.4                                                                              ˜6.1/1.6/1                                                                     sodium ferrate or                                                                         ignited-slow burning rate                                           sodium aluminate                                 48.9                                                                              Al.sub.2 O.sub.3                                                                      31.3                                                                               Fe.sub.2 O.sub.3                                                                      19.9                                                                              ˜2.5/1.6/1                                                                     sodium ferrate or                                                                         ignited-very slow burning                                           sodium aluminate                                                                          rate                                  25.2                                                                              Al.sub.2 O.sub.3                                                                      46.1                                                                               Fe.sub. 2 O.sub.3                                                                     28.7                                                                              ˜1/1.8/1.1                                                                     sodium ferrate or                                                                         no ignition                                                         sodium aluminate                                 70.0                                                                              Al.sub.2 O.sub.3                                                                      23.5                                                                               Fe.sub.2 O.sub.3                                                                       6.5                                                                              ˜10.8/3.6/1                                                                    sodium ferrate or                                                                         no ignition with sustained                                          sodium aluminate                                                                          burning                               54.0                                                                              Al.sub.2 O.sub.3                                                                      36.1                                                                               Fe.sub.2 O.sub.3                                                                       9.9                                                                              5.5/3.6/1                                                                            sodium ferrate or                                                                         ignited, but would not                                              sodium aluminate                                                                          sustain combustion                    23.6                                                                              Al.sub.2 O.sub.3                                                                      60.4                                                                               Fe.sub.2 O.sub.3                                                                      16.0                                                                              1.5/3.8/1                                                                            sodium ferrate or                                                                         no ignition                                                         sodium aluminate                                 27.4                                                                              Al.sub.2 O.sub.3                                                                      25.7                                                                               Fe.sub.2 O.sub.3                                                                      46.9                                                                              1.1/1/1.8                                                                            sodium ferrate or                                                                         no ignition with sustained                                          sodium aluminate                                                                          combustion                            64.9                                                                              CaCO.sub.3                                                                            24.3                                                                               Fe.sub.2 O.sub.3                                                                      10.8                                                                              6/2.2/1                                                                              Na.sub.2 CO.sub.3 +CaOFe                                                                  ignited-moderate burning                                                       rate                                  77.8                                                                              CaMg(CO.sub.3).sub.2                                                                   9.3                                                                               Fe.sub.2 O.sub.3                                                                      12.9                                                                              8.4/1/1.4                                                                            Na.sub.2 CO.sub.3 +MgO+CaO+Fe                                                             ignited-moderate burning                                                       rate                                  85.7                                                                              Fe.sub.2 O.sub.3                                                                      14.26                                                                               --    -- 6/1   Na.sub.2 O+Fe                                                                             ignited easily-fairly rapid                                                    burning rate                          82.0                                                                              Fe.sub.2 O.sub.3                                                                      18.0                                                                                --    -- 4.56/1                                                                               Na.sub.2 O+Fe+Fe.sub.2 O.sub.3                                                            ignited-less rapid burning                                                     rate                                  71.1                                                                              Fe.sub.2 O.sub.3                                                                      28.9                                                                                --    -- 2.46/1                                                                               Na.sub.2 O+Fe+Fe.sub.2 O.sub.3                                                            ignited-moderate burning                                                       rate                                  54.3                                                                              FeCO.sub.3                                                                            45.7                                                                                --    -- ˜1/1                                                                           Na.sub.2 CO.sub.3 +Fe                                                                     ignited-slow burning rate             45.3                                                                              FeCO.sub.3                                                                            42.4                                                                               Fe.sub.2 O.sub.3                                                                      12.3                                                                              3.7/3.4/1                                                                            Na.sub.2 CO.sub.3 +Fe+Fe.sub.2 O.sub.3                                                    ignited-slow burning rate             57.7                                                                              FeCO.sub.3                                                                            32.4                                                                               MgCO.sub.3.×H.sub.2 O                                                            9.9                                                                              5.8/3.3/1                                                                            Na.sub.2 CO.sub.3 +MgO+Fe                                                                 ignited-slow burning rate             51.4                                                                              FeCO.sub.3                                                                            28.8                                                                               MgCO.sub.3.×H.sub.2 O                                                           19.8                                                                              2.6/1.5/1                                                                            Na.sub.2 CO.sub.3 +MgO+FeO                                                                no ignition with sustained                                                     burning                               46.0                                                                              MgCO.sub.3.×H.sub.2 O                                                           40.6                                                                               Fe.sub.2 O.sub.3                                                                      13.4                                                                              3.4/3.0/1                                                                            Na.sub.2 CO.sub.3 +MgO+FeO                                                                no ignition with sustained                                                     combustion                            57.7                                                                              SiO.sub.2                                                                             42.3                                                                                --    -- 4/3   Na.sub.2 SiO.sub.3 +Si.sub.3 N.sub.4                                                      ignited-very rapid burning                                                     rate                                  __________________________________________________________________________

As can be seen by comparing the theoretical reactions and the actual experimental reactions noted in Table I, some differences between the experimental result and the theoretical expectations are observed. For example, in the reaction of aluminum fluoride with sodium azide, the reaction does not proceed to the production of aluminum nitride and sodium fluoride but rather Na₃ AlF₆ and AlN is produced. Also, as can be seen from the above table, it is not always possible to predict which combinations of materials will function properly according to this invention and in what particular relationship they may occur. For example, in the system using lithium azide, aluminum oxide, silicon dioxide, and 1 percent fiberglass reinforcement, no combustion was obtained when the mole ratio of the materials were respectively 12/6/39 and 25/6/90, yet good residue retention was obtained with a mole ratio of 24/6/39. It has not been determined if this was because of the increased amount of sodium azide, decreased amount of silicon oxide or some combination of the two with the latter being the most probable. Thus, while the applicant has not tested every combination of materials in all proportions to determine which do and which do not function to produce a gas generator grain capable of generating nitrogen in self sustained manner at reasonable temperatures, this disclosure is believed adequate to teach workers skilled in the art a new type of composition and how generally to determine which materials will work. Nevertheless, some experimentation, well within ordinary skill, will be required by workers skilled in the art to select the precise composition for any particular combination of materials within the scope of this disclosure and the claims but which are not specifically disclosed by example herein. While this invention has been illustrated with respect to numerous examples, the invention is not limited thereto and various modifications can be made by workers skilled in the art without departing from the scope of the invention which is limited only by the following claims wherein: 

We claim:
 1. A gaseous nitrogen generating composition comprising a mixture of a metal azide and a material selected from the group consisting of: Fe₂ O₃, AlF₃, Al₂ O₃ +Fe₂ O₃, B₂ O₃, CuCl, CuO, Fe₃ O₄, MnO₂, SiO₂, TiO₂ and mixtures thereof, said materials being oxides and salt of elements lower in the electrochemical series of the elements than the metal component of the azide and being capable of liberating sufficient heat upon exothermic reaction with said azide to maintain a self-sustained combustion.
 2. The composition of claim 1 wherein said metal azide is selected from the group consisting of alkali metal azides.
 3. The composition of claim 2 further comprising a material selected from the group consisting of carbon-nitrogen compounds, metal oxalates and metal carbonates.
 4. The composition of claim 3 wherein said carbon-nitrogen compounds, metal oxalates and metal carbonates are selected from the group consisting of tetracyanoethylene, Li₂ C₂ O₄, Na₂ C₂ O₄, MgC₂ O₄, CaCO₃, FeCO₃, MgCO₃, MgCa(CO₃)₂ and mixtures thereof.
 5. The composition of claim 4 further comprising an oxidizing agent selected from the group consisting of NaNO₃, NaClO₄, LiNO₃, LiClO₄, NaClO₃, Mg(ClO₄)₂.
 6. The composition of claim 4 further comprising a material selected from the group consisting of FeO(OH), Mg(ClO₄)₂.6H₂ O, (COOH)₂.2H₂ O and oxamide.
 7. The composition of claim 6 further comprising a material selected from the group consisting of NaNO₃, NaClO₄, LiNO₃, LiClO₄, NaClO₃ and Mg(ClO₄)₂.
 8. The composition of claim 1 wherein said azide is sodium azide and said material is Fe₂ O₃.
 9. The composition of claim 1 wherein said azide is sodium azide and said material is CuCl.
 10. The composition of claim 1 wherein said azide is sodium azide and said material is Al₂ O₃ +Fe₂ O₃.
 11. The composition of claim 1 wherein said azide is sodium azide and said material is SiO₂.
 12. The composition of claim 1 wherein said azide is sodium azide and said material is CuO.
 13. The composition of claim 1 wherein said azide is sodium azide and said material is B₂ O₃.
 14. The composition of claim 1 further comprising a fiberous binder.
 15. The composition of claim 7 further comprising a fiberous binder. 